Experimental Investigation of Hypoplastic Left Heart Syndrome (HLHS) Brandon Goodman, Undergraduate ME; James Buchholz, Ph.D.; Department of Mechanical Engineering, University of Iowa, Iowa City, IA INTRODUCTION Hypoplastic Left Heart Syndrome (HLHS) is a rare but serious congenital heart defect in which the left ventricle fails to develop fully. Several treatments are available to correct the malformation, but they are highly invasive with no guaranteed outcome. Despite successful correction, quality of life remains at a minimum and life expectance is only half of the general population’s. Without treatment, the condition is fatal [1]. Both genetic and environmental factors are believed to cause HLHS. One theory suggests that abnormal flow patterns in the ventricle brought on by environmental stressors alter sheer stresses on cardiac cells during development ergo altering their overall development. To test this theory a means of cardiac wall stress measurement was explored. METHODOLOGY Left Heart Construction For the initial construction of the artificial left heart, both 2 and 3 dimensional models where considered. Ultimately the 2-D planar geometry was selected for its simplicity, especially pertaining to the kinematic equations governing flow in the model, and the investigator's desire to establish validity in the experimental method. The heart model was designed using Pro Engineer® and the negative was molded via rapid prototyping. The atrium and ventricle were modeled using an approximate semi-elliptical cross-section. Again, for simplicity, a 2-D bi-leaflet valve was used in place of an actual 3-D tri-leaflet model. This valve was made of.00075" shim stock. The box was constructed using 7/16" acrylic plates enclosing dimensions 3"X3.81"X5". As leaking was an issue, the final heart had 4 sides permanently cemented together with 2 removable section for model cleaning and valve exchange. Figure 1. Final Heart Model (left) and Initial Test Model (right) Particle Image Velocimetry Testing apparatus seeded with micron-sized tracer particles Two spatially –coincident laser sheets separated by short time interval shown through the central axis of the model heart Prior experiments have been performed matching indexes of refraction for silicone and acrylic Figure 2. Final Left Heart Model and Pump Assembly RESULTS Digital Particle Image Velocimetry Diagram DISCUSSION PIV methods require additional refinement Minor issues with laser scattering caused by bubbles set in the silicone mold Flow through jet more closely simulated steady state jet flow than pulsatile flow Expected vortex formation off the tips of the mitral valves similar to what is seen in (Fig. 3, c) where there was none Out of plane fluid motion negatively effected the PIV’s ability to perform a 2-D planar analysis of the model’s center region CONCLUSION A 3-dimensional model is required to more accurately model the dynamics of the human fetal heart Concurrent entrance and exit flow diminished the experiments ability to establish 2 dimensionality Revisiting the 2 dimensional model will require greater control of inflow and outflow ACKNOWLEDGMENTS Special thanks to Prof. Buchholz for his help and patience as a mentor Thanks to Brittany Anderson for her aid on the project during the summer Thanks to Kathleen Lin for suggestions and help with the Vivitro setup LOOKING FORWARD Figure 4. PIV Model Setup Figure 3. Vortical Flow in vivo (a,b), and in vitro (c) Mitral Valve Pulmonary Veins Left Atrium Future 3 dimensional model testing using the Vivitro Left Heart System System allows for valve exchange Possesses peripheral resistance and supplementary characteristic compliances to simulate cardiovascular properties and resistances More accurately simulates pulsatile flow for aide in mitral valve vortex formation Pump Construction Closed system water pump 4 pulmonary inlet tubes ran the length of the model, each regulated by needle values (Fig 2. Pump Setup) Final model utilized 4 aortic outlets running the length of the model (Fig 1.) Pump stroke of 2” used to displace 70% of the ventricle’s volume LabVIEW ™ used to run the motor controls Aortic Outlets REFERENCES Figure 7. Vivitro Labs Model Left Heart System Aorta 1.Anderson, R. H., Pozzi, M. M., & Hutchinson, S. (2005). Hypoplastic Left Heart Syndrome. London: Springer. 2.Gharib, M., Rambod, E., Kheradvar, A., Sahn, D., & Dabiri, J. (2006). Optimal vortex formation as an index of cardiac health. Pasadena, CA: California Institute of Technology. 3.Raffel, M., Willert, C. E., Wereley, S. T., & Kompenhans, J. Particle Image Velocimetry: A Practical Guide (éd. 2nd Edition). Springer. 4.Willert, C. E., & Gharib, M. (1991). Digital particle image velocimetry. Dans Experiments in Fluids (pp. 10, ). Dept. of Applied Mechanics and Engineering Sciences, University of California, San Diego. Aorta Ventricle Figure 3. PIV Model Diagram Atrium Ventricle